2

我想UNION ALL在 3 个不同的表上使用，通过使用将它们合并到一个表中SELECT INTO。

表 1、2 和 3 分别有 15、7 和 8 列。

那么，有没有办法让我使用UNION ALL表 2 和表 3 默认为 NULL 缺失的列，而不单独对它们进行分类？

例如，我一直在做：

SELECT  NULL as [Company_Code], NULL as [Doc_Code], 
NULL as [Doc_Type], [H ID] as [Document_No] FROM [table_2] 
INTO BIG_TABLE
UNION ALL 
SELECT
[Document Company] as [Company_Code], [Document Company] as [Doc_Code], 
[Doc Type] as [Doc_Type], NULL as [Document_No]
FROM [table_3]

这样，列数匹配，我可以将它们联合起来。

但是，我想知道是否有一种方法可以避免繁琐的机制来避免为丢失的每一列插入 NULL，并一次性自动完成？

谢谢。

4

4 回答 4

4

简而言之，没有。 Union结果集必须具有相同数量/数据类型的列。如果你想让剩余的集合填充null，最简单的方法是做这样的事情 -

select col1
, col2
, col3
, col4
from tbl1

union all

select null as col1
, null as col2
, null as col3
, null as col4
from tbl2
于 2015-12-14T03:36:56.770 回答
1

联合应该在另一个选择中

SELECT * FROM(
    SELECT col1, col2 FROM test_table1
  UNION ALL
    SELECT col1, col2,col3 FROM test_table2
);

结果将是 col1 和 col2 不匹配的列被跳过

于 2015-12-14T03:36:46.770 回答
0

我仍然建议使用@iliketocode。

动态列根据您的要求生成

这只是另一种选择，但完全是您想要的动态（只需要一些时间来执行而不是上面的答案）。要在不定义每一列的情况下实现结果，您可以创建动态查询，通过循环自动将列添加为空。

我面临同样的问题，由于时间短，我已经完成了上述工作。但是今天我填写了正确的解决方案（当时我没有这样做）并且我为你创建了一个你想要的样本，我希望这会对你有所帮助。

--create table t1 (col1 int , col2 int, col3 int)
--create table t2 (col1 int , col2 int, col3 int, col4 int)

--insert into t1 values (1,11,111), (2,22,222)
--insert into t2 values (1,11,111,1111), (2,22,222,null)

--Step 1 - Declaration of variable
Declare @NoOfColumnForUnion int = 5

declare @T1TableColumnList nvarchar(max) ='' ,@T2TableColumnList nvarchar(max) ='' , @colName nvarchar(500) , @test cursor

--Step 2 - Get the column list of first table i.e. t1 and store into @T1TableColumnList variable
set @test = cursor for 
                select name from syscolumns 
                where id = object_id('t1')                 

open @test
fetch next from @test into @colName
while @@fetch_status = 0 
begin
    set @T1TableColumnList = @T1TableColumnList + @colName + ','

    fetch next from @test into @colName 
end

set @T1TableColumnList = left( @T1TableColumnList , len(@T1TableColumnList )-1)

close @test
deallocate @test

--Step 3 - Get the column list of Second table i.e. t2 and store into @T2TableColumnList variable
set @test = cursor for 
                select name from syscolumns 
                where id = object_id('t2')                 

open @test
fetch next from @test into @colName
while @@fetch_status = 0 
begin
    set @T2TableColumnList = @T2TableColumnList + @colName + ','

    fetch next from @test into @colName 
end

set @T2TableColumnList = left( @T2TableColumnList , len(@T2TableColumnList )-1)

close @test
deallocate @test

--Step 4 - Check the length of column list to add null columns or remove columns
--First table check
Declare @T1lengthofColumnList int
set @T1lengthofColumnList =  (len(@T1TableColumnList) - len(replace(@T1TableColumnList, ',', '')) ) + 1

--add columns
if( @T1lengthofColumnList  < @NoOfColumnForUnion)
 Begin  
    While (@T1lengthofColumnList  < @NoOfColumnForUnion)
     Begin
        set @T1lengthofColumnList = @T1lengthofColumnList + 1
        Set @T1TableColumnList = @T1TableColumnList +  ', null col' + cast( @T1lengthofColumnList as varchar(10))
     End
 End
--remove columns
Else if( @T1lengthofColumnList  > @NoOfColumnForUnion)
 Begin
    While (@T1lengthofColumnList  > @NoOfColumnForUnion)
     Begin
        set @T1lengthofColumnList = @T1lengthofColumnList - 1       
        Set @T1TableColumnList = LEFT(@T1TableColumnList, LEN(@T1TableColumnList) - CHARINDEX(',',REVERSE(@T1TableColumnList))) 
     End
 End

--Second table check
Declare  @T2lengthofColumnList int
set @T2lengthofColumnList =  (len(@T2TableColumnList) - len(replace(@T2TableColumnList, ',', '')) ) + 1

--add columns
if( @T2lengthofColumnList  < @NoOfColumnForUnion)
 Begin  
    While (@T2lengthofColumnList  < @NoOfColumnForUnion)
     Begin
        set @T2lengthofColumnList = @T2lengthofColumnList + 1
        Set @T2TableColumnList = @T2TableColumnList +  ', null col' + cast( @T2lengthofColumnList as varchar(10))
     End
 End
--remove columns
Else if( @T2lengthofColumnList  > @NoOfColumnForUnion)
 Begin
    While (@T2lengthofColumnList  > @NoOfColumnForUnion)
     Begin
        set @T2lengthofColumnList = @T2lengthofColumnList - 1       
        Set @T2TableColumnList = LEFT(@T2TableColumnList, LEN(@T2TableColumnList) - CHARINDEX(',',REVERSE(@T2TableColumnList))) 
     End
 End

--Step 5 - create dynamic query and execute
DECLARE @template AS varchar(max)

SET @template = 'select ' + @T1TableColumnList + '  from t1 union all ' 
+ ' select ' + @T2TableColumnList + '  from t2 '

select @template 

EXEC (@template)


--drop table t1
--drop table t2
于 2015-12-14T07:45:13.213 回答
0

使丢失的列无效的最佳方法是使用null 作为您希望查看其空列的column_name ，如下所示：...

    SELECT id as var1, mgr_id as var2,name as var3 into exp_test1 FROM
 emp123    UNION ALL
      SELECT null as employeeid, null as departmentid,null as lastname FROM employee
于 2015-12-14T05:18:39.770 回答